Project Summary/Abstract In spite of the evidence supporting the involvement of the glutamatergic system in Alzheimer?s disease (AD), research has focused on indirect measures of glutamate (Glu) involvement, mainly through increased downstream pathways related to excitotoxicity, without addressing possible changes in extracellular Glu occurring during disease progression. Knowledge of basal and phasic extracellular Glu levels and clearance kinetics would allow us to establish an early biomarker, better determine and explore novel therapeutic targets, and establish the opportune treatment window that has the potential to alter AD progression. Until recently, research measuring extracellular Glu levels has been limited because few techniques are capable of in vivo analysis within small sub-regions of the brain. We have developed a MEA that, when combined with electrochemistry, has the ability to measure micromolar changes in basal and phasic extracellular Glu with high temporal (msec) and spatial (micron) resolution during acute and chronic recordings. We plan to use this technique to address our central hypothesis that alterations in extracellular Glu in awake animals occur prior to cognitive decline and neuropathology associated with AD, and that A? accumulation with age potentiates these changes resulting in the cognitive decline typical in AD. This hypothesis will be evaluated using a novel knock-in mouse model of AD, APPNL-F/NL-F mice, and APP/PS1 mice, and their respective controls at 2-4, 8-10, and 18-20 months of age. At these ages, one cohort of mice will undergo cognitive evaluation using the Morris water maze followed by awake stimulus (KCl)-evoked Glu recordings in the CA1 region of the hippocampus. These studies will help us determine if basal Glu and Glu release (presynaptic) and uptake (glia and postsynaptic) kinetics are altered in AD mice and if so, how and when these alterations occur over the continuum of cognitive and pathophysiological decline. Next, to determine if alterations in Glu neurotransmission is behaviorally detrimental, we will examine a second group of mice at the same ages and hippocampal sub-region during a memory related task, the spontaneous alternation y maze. This will allow us to determine the impact of aging and AD progression on formation and recall of memories in the form of phasic Glu measurements. Taken together, we anticipate that these studies will give us valuable insight into the role of Glu as an early biomarker, a mechanism for disease progression, a site for potential novel therapeutic targets, and optimal intervention timeframes for AD.